The new tp-link Archer T3U Mini Wireless MU-MIMO USB WiFi Adapter I purchased was a challenge to install on an older HP desktop PC with USB 2.0. The installation was uneventful until I tried to access the router about 7 feet away. Initially, the device appeared in the Windows 10 WiFi window but did not connect when clicked on with the mouse. Then the notice said no WiFi devices found. When I tried again, it said connecting but did nothing. I clicked on the network again and it connected and then disconnected. After the third or fourth try it connected. Frustration ensued.
I checked the tp-link website for a solution and other websites for a solution. No solid solutions worked. Finally, I contacted live support at tp-link. I was told to change the router to a specific channel in the 5 GHz band above channel 144. While I was in the router setup, I also noticed a 20 MHz bandwidth selected for 5 GHz. Since the 2.4 GHz band was at 20 MHz bandwidth, I changed the 5 GHz bandwidth to 40 MHz to accommodate the higher speed. After the changes were done and the router rebooted, I had a solid connection with the Archer T3U and a single click to connect to the network. I did not know at the time which of the changes solved the problem.
The next day, I did a Google search on the WiFi channels and found that 5 GHz WiFi should have a 40 MHz channel bandwidth. Armed with that knowledge, I changed the router back to Auto channel mode in the 5 GHz band from the 149-165 channel setting. We already had a static channel for 2.4 GHz. After rebooting the router, the Archer T3U worked as well as with 149-165 channel setting. In my case, the solution was just changing the router to 40 MHz bandwidth for the 5 GHz band. We had the only nearby WiFi network on the 5 GHz band. In the process of all of this, I changed the power settings and Device Manager to not turn off power to the T3U USB device to prevent problems when the PC wakes up from hibernation. So far, so good. Speed is dependent on the speed test site being used, but 5 GHz over 150 mb/sec on a 200 mb/sec connection.